Modulation; A better option for communication

3년 전

It's been quite some time my brother went back to school. You see, his school is in a different state, though in the same country. And the other day I tried contacting him; I went out of the house and shouted all I needed him to hear from where ever he is. But there is one thing that still bothers me - I can't really tell if he heard me or not. What do you think?

I know you think am crazy, but am not. So you believe that he (my brother) won't hear me this way. And why is that? You still don't know? Let's find out why and what can be done to help




Pixabay

Sound

When we speak, the air around our mouth vibrates to and fro, and this "vibrating air" is what carries the message we wish to pass across to someone standing close by. Because of this, we can regard our speech as alternating signal (to and fro).

From our secondary school, we are taught that alternating signals are characterized by - frequency, amplitude, wavelength etc. And in the same way, our speech is also characterized by this three concepts. Just to give a quick recall as to what they mean

  • Frequency - Is the number of complete revolutions or cycles of a signal in a second in Hertz (Hz)
  • Amplitude - Is the highest displacement of a signal in terms of voltage, height etc.
  • Wavelength - Is the distance between two similar peaks of a signal in meters (m)

So how do this three play a role in our speech?

For the most part, amplitude determines how loud our voice can get, meaning that a higher amplitude would result in a louder voice while a lower amplitude would result in a quieter voice. Amplitude could also be seen as the amount of energy our speech carries or can carry.

Going back to our initial discussion: One possible solution to the present problem could be for me to try out the experiment again but this time around to increase the amplitude or loudness of my voice. This could probably help increase the distance my voice would travel but I doubt if my brother who is over 1000km away would still hear me.

The loudest (verified) human scream was 129 dB (decibels) performed by Jill Drake, a woman. Source

Comparing this with the list of other sound source and their equivalent values in decibel published in this article by Vigilantpps, 129dB is nearly equivalent to the sound of a power drill or jackhammer. And on an average, a power drill as most of us may have experienced doesn't"t travel very far. One obvious reason is the fact that damping would occur, that is, the reduction of amplitude or energy with an increase in distance and time.

Another possible solution may be to increase the frequency or pitch of my voice. But how high do you think the pitch of a man's voice could get?

The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz source

This is still very low compared to the thousands of Hz that would be required to send the information I want to pass across such distance. Even radio waves (electromagnetic waves) require as much as 3Khz to 300Ghz to travel such distance.

What better option could there be?

One better option would be to convert the message in Sound/Speech to an equivalent in electrical form (electrical signal), and manipulate the frequency characteristic of the wave and radiate them across, but this will only distort, alter or worst destroy the message. Though the message is now in electrical form, the message is characterized by its properties and any change would end up leaving us with electrical signals with no message.



Modulation Image by Robert Couse-Baker (CC BY 2.0)

An option that works

After trying so many things, the best option seems to be modulation. So what is modulation?

We know that the message or signal or message signal that I/we wish to send across cannot travel far because of its low frequency. Yes? Now modulation seeks to find a way to increase the frequency of the message signal without altering the actual message.

Modulation achieves this by introducing a signal with a high frequency - carrier signal capable of covering/travelling the distance in question - and impressing the message on it, So that at the end we have a new signal with a high frequency capable of traveling such distance and also contains the message that is to be passed across.

This is accomplished with an apparatus called the modulator. The modulator changes the/some characteristics (amplitude, frequency etc.) of the carrier signal with respect to or in accordance with the amplitude of the message signal (modulating signal) in other to produce a new signal of high frequency called the modulated signal capable of traveling very far distances.

The message signal contains the message (information) whereas the carrier signal contains no message (information). The sole purpose of the carrier signal is to transmit the message across and at the receiving end the message signal can be separated from the carrier signal by a process known as demodulation. The key is to get the message across.

Because of the possibility of modulating (changing) different characteristics of the carrier signal, different modulation techniques are born. Some of the modulation techniques commonly used include the Amplitude modulation, Frequency modulation, Phase modulation or as they are more commonly called AM, FM and PM respectively.

Choosing which modulation technique to use would depend on the task at hand, the distance to travel or the quality of the message that will be transmitted.

Amplitude modulation is best suited for long distance transmission as they seem to cover long distances before any significant signal damping may occur. But because noise is a variation of amplitude, AM signals tend to pick up noise through the transmission channel.

Whereas frequency modulation is better suited for "quality of information". Since noise is a variation of amplitude and not frequency, FM signals do pick up noise. Also, FM signals are stronger in terms of signal strength compared to the AM.



A modulator. Image by Peter Knorr Wikimedia Commons

Summarizing

In other to transmit signals over long distances modulation seems to be the best choice as it offers the means of transferring our message without having to alter or change our message signal characteristics by letting us rather modulate a high-frequency signal known as the carrier signal and by so doing impressing our message on the carrier signal.

An added advantage is that at the receiving end we can separate our message from the carrier signal by a process known as demodulation - kinda like the reverse of modulation.

Thanks for reading


References:


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